In land levelling and earthmoving applications, a ground scraper is often employed. Typically, the ground scraper is towed behind a powered vehicle such as a tractor to excavate ground material and level a ground surface. The excavated ground material is then transported to another location. Generally, ground scrapers comprise a cutting edge, referred to as a blade or bit, of adjustable height that is lowered to engage and excavate the ground material and a bowl rearward of the blade in which the excavated ground material is collected as the ground scraper is pulled along.
Once a required volume of ground material has been excavated to level the ground surface or the bowl is full, the cutting edge is raised clear of the ground surface to cease excavation and a gate or “apron” closes an opening at the front of the bowl to retain the excavated ground material in the bowl. Typically, the excavated ground material is that transported to a dumpsite where the apron is opened and a hydraulic ejection ram drives a door at a rear of the bowl forward to expel the excavated ground material from the bowl. Alternatively, in some scrapers, the bowl pivots to tip the excavated material from the bowl.
One type of ground scraper includes a rigid hitching arm forward of the bowl for coupling the scraper to the powered vehicle and a set of wheels, often referred to as walking wheels, rearward of the bowl to support the scraper and enable the scraper to roll along the ground. Whilst this type of scraper is very good at light ground levelling and may be drawn quickly over the ground, the relatively small size of the bowl and the opening into the bowl make it unsuitable for large earthmoving applications. Typically, in such ground scrapers the apron only opens a small distance, which prevents all of the excavated ground material being expelled from the bowl in a single pass of the door or pivot of the bowl. Consequently, the door needs to be driven back and forth a number of times or the bowl needs to be pivoted numerous times to expel or dislodge all of the excavated ground material from the bowl. This is particularly so when the excavated ground material has a high moisture content.
Another problem with prior art aprons is that once the bowl is relatively full, the apron is incapable of forcing any more excavated ground material into the bowl. Similarly, excavated ground material that has been scraped up often accumulates in front of the cutting edge as the scraper moves along and the excavated ground material does not collect in the bowl. Some prior art aprons are incapable of capturing this excavated ground material in the bowl and it has to be left behind. This results in mounds of ground material on an otherwise levelled ground surface that have to be collected once the bowl has been emptied, which is inefficient. Typically, between 20% to 40% of the scraped ground material can be left behind with this type of scraper when the ground material is loose or dry.
A further problem associated with this type of scraper is that the workings of the bowl are prone to clogging when used in wet conditions. Specifically, this particular type of ground scraper has many voids and regions in which ground material can accumulate and be compacted. Consequently, earthmoving and levelling operations may need to be suspended until the scraper is unclogged.
Another problem with some types of scrapers is the relatively large separation between the sets of walking wheels, which makes it difficult to turn the scraper. This, in turn, causes the scraper to rip up the levelled ground surface, often creating ruts of 0.3 m or more and necessitating re-levelling of the ground surface.
The wheels of other types of scrapers are fixed in position and when some of the wheels are not supporting the scraper on the ground, such as when the scraper is used on undulating terrain, high stress can be imparted on one or more of the wheels and/or the frame of the scraper.
Furthermore, most scrapers are susceptible to “duck-walking” on undulating terrain, which impairs the levelling capacity of the ground scraper and the operator must slow down to overcome the duck-walking, thus slowing down the levelling process.
A yet further drawback of the numerous prior art ground scrapers is their complexity of design. Many have a large number of different parts which complicates maintenance and repairs and increases the cost of the scraper.
A range of ground scrapers are disclosed in: U.S. Pat. No. 2,224,438 (Le Bleu), U.S. Pat. No. 3,574,960 (Peterson et al), U.S. Pat. No. 4,393,608 (Hodge), U.S. Pat. No. 6,092,316 (Brinker), U.S. Pat. No. 6,041,528 (Broach), U.S. Pat. No. 5,839,212 (Brinker) and U.S. Pat. No. 6,910,289 (Moyna et al.); United States Patent Application No. 2002/0078606 (Grummett); and former Soviet Union abstracts SU 768884 (Sibe Auto Road Inst.), SU 996648 (Sibirsk Automobil Dorozh), SU 1216292 (Moscow Auto Road Constr.), SU 12571.41 (Mogil Mech. Eng. Inst.) and SU 1602934 (Shavolov et al.). Whilst these scrapers perform theft task satisfactorily, each suffers from one or more of the aforementioned problems.
The applicant has ameliorated one or more of the aforementioned problems by virtue of their ground scraper as disclosed in WO 2006/006318, which is herein incorporated by reference in its entirety. However, the applicant has recognized that further refinements of their invention are required to improve the performance of their ground scraper.
It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.